Does the motor have to be in water if you are just cranking it briefly,without ruining the water pump? As in compression test or checking starter etc.?
spinning the impeller without water to lubricate it may not damage it while just cranking, however why take a chance. put muffs on it.
if it is a new to you motor that you are checking out because you are considering buying, doesnt mater, as your first order of business is to put in a new water pump anyway.
It is always recommended to have cooling water connected either with a tub or bucket or muffs with garden hose. Anytime the impeller rotates without water which it uses as lubricant it gets damaged. Slowly but surely it will fail prematurely and usually that happens when you are out at the lake or really far from shore!
S. A. Baker, I have to say that is a very good question! I am sure most of us don't use water when doing a standard compression test. I know I didn't. But then I already had plans to change out the water pump total assembly. But to be honest, I'd think most don't put the engines on the muffs or in water buckets to do compression testing. And I also don't think a few slow revolutions to get compression readings would do any serious damage because the engine is spinning so slow in comparison to even idle speeds. So I don't see the rubber impellor melting or sanding down much if any amount. But that is just me...JMHO!
Thanks guys.. Just checking a few things out with no intention of running it. Likely won't even run it before it's time to store for the winter. It's already like late fall here! Just got the boat two weeks ago... Finally have everything repaired ,rewired and up to my picky standards. A little late in the year here to dig into a water pump! I just got the shifting issue sorted out!